Gasifiable casting care

ABSTRACT

A casting pattern disposed in a molded material and having the configuration of the article to be cast. A core member is located within the outer body member and has the configuration of a cavity to be formed and the casting. The outer body member and the core member are each composed of a material gasifiable substantially without residue upon being subjected to the elevated temperature of a molten casting charge. A first layer of refractory gas permeable material covers the outer body member and remains solid at the elevated temperature of the molten casting charge. A second layer of refractory material covers the entire outer surface of the core member which is exposed to the body member for preventing contact between the casting charge and the core member and being operative to retard the transmission of heat from the molten casting charge to the core member to prevent the gasification of core member until a portion of the metal adjacent the second layer has solidified.

United States Patent Wittmoser et a].

[541 GASIFIABLE CASTING CARE Full Mold Process, Inc., Lathrup Village,Mich.

[22] Filed: Aug. 8, 1969 [21] Appl. No.: 871,096

Related U.S. Application Data [73] Assignee:

[60] Division of Ser. No. 615,866, Nov. 1, 1966, Pat. No.

3,498,360, which is a division of Ser. No. 298,678, July 30, 1963, Pat.No. 3,314,116, which is a continuation-in-part of Ser. No. 270,085, Apr.2, 1963, abandoned.

[52] U.S. Cl ..l64/369, 164/246 [51] Int. Cl. ..B22c 9/10, B22c 7/02[58] Field ofSearch ..164/34,35,4l,43,47,138, 164/246, 235, 369,24, 30

[5 6] References Cited UNITED STATES PATENTS 2,756,475 7/1956Haninketal. ..164/30 [15] 3,654,987 51 Apr. 11, 1972 Primary Examiner-R.Spencer Annear Attorney-Ronald E. Barry [57] ABSTRACT A casting patterndisposed in a molded material and having the configuration of thearticle to be cast. A core member is located within the outer bodymember and has the configuration of a cavity to be formed and thecasting. The outer body member and the core member are each composed ofa material gasifiable substantially without residue upon being subjectedto the elevated temperature of a molten casting charge. A first layer ofrefractory gas permeable material covers the outer body member andremains solid at the elevated temperature of the molten casting charge.A second layer of refractory material covers the entire outer surface ofthe core member which is exposed to the body member for preventingcontact between the casting charge and the core member and beingoperative to retard the transmission of heat from the molten castingcharge to the core member to prevent the gasification of core memberuntil a portion of the metal adjacent the second layer has solidified.

3 Claims, 10 Drawing Figures I INVENTORS. Adolbert Wittmoser JohannaSchode Erich Krzyzonowsk'l F I G. l

\NE UFLQ SHEET 1 [1F 3 Fl G. 2

Attorney PATENTEDAPR 1 1 I972 PATENTED 1 I9 3.654.987

SHEET 2 OF 3 FIG.6

73G 73d 73 C 73b INVENTORS Adolbert Wmmoser Johannes Schode ErichKrzyzonowski W4 WM Attorney PATENTEDAPR 1 1 I972 SHEET 3 []F 3 FIG; I0

I N VENTORS Adolbert Wmmoser Johannes Schcde Erich KrzyzanowskiGASIFIABLE CASTING CARE This application is a division of our copendingapplication Serial No. 615,866, filed Nov. 1, 1966, now U.S. Pat. No.3,498,360, which is a division of application Ser. No. 298,678, filedJuly 30, 1963, now U.S. Pat. No. 3,314,116, which is a continuation inpart of application Ser. No. 270,085, filed Apr. 2, 1963, now abandoned.

The present invention relates to a casting arrangement, and moreparticularly, the present invention is concerned with improvementsrelating to gasifiable patterns.

According to conventional casting procedures a pattern having the shapeof the casting to be made and consisting of wood-metal, wax, syntheticresin etc. is embedded in an appropriate molding material or moldingsand respectively, in the mold. After packing the molding material toform a mold body, the pattern is removed and the melt is poured into thecavity which remains in the molding material. For this procedure lostpatterns can be applied that means patterns which are destroyed afterembedding, for example when employing a wax pattern which is melted out.

It is another object of the present invention to improve the usefulnessof gasifiable casting patterns.

It is a further object of the present invention to provide improvedgasifiable casting patterns which can be produced and used in a simpleand economical manner.

It is a further object of the present invention to provide castingarrangements including improved feeder head patterns.

Other objects and advantages of the present invention will becomeapparent from a further reading of the description of the appendedclaims.

The present invention includes a method of casting, comprising the stepsof embedding in a mold body a form which is gasifiable substantiallywithout residue on subjection to a molten casting charge and which isshaped for exact reproduction as a casting and the surface of which iscovered with a layer consisting of a solid material which remains solidand is gas permeable at the temperature of the molten casting charge,providing in the mold body and in the layer a passage for a moltencasting charge to the embedded form, and pouring into the passage amolten casting charge for gasifying and replacing the embedded form inthe mold body.

According to the present invention, the outer surface of the pattern isprovided with a shell-like, substantially incombustible coat or layerwhich will not be affected by the temperature of the penetrating meltand which preferably will be highly permeable to gas or becomingpermeable to gas during the pouring process. It is, also within thescope of the present invention, to incorporate in the cellular plasticcasting pattern solid or gaseous materials which will act on, or reactwith, the molten casting charge, for instance in the case of a moltenmetal casting charge, a material which will cause a metallurgicaltreatment of the casting metal.

The present invention thus overcomes the difficulties experienced up tonow in connection with gasifiable casting patterns and will result inthe production of cast bodies or castings of the desired surfacestructure, even when embedded in a loose molding material such as dryquartz sand which need not contain any binder. Even metal shot orsimilar materials may be used as the molding material. Furthermore,according to the present invention, not only an improvement of thesurface of the casting is achieved but also of its inner structure whichmay be influenced by the incorporation of suitable materials in thegasifiable cellular plastic casting pattern.

The shell-like, substantially incombustible coat or layer on the outerface of the cellular plastic pattern will also advantageously act as abarrier preventing the escape of alloying and similar materials whichmay have been incorporated in the cellular gasifiable plastic castingpattern. In other words, when upon contact with the molten castingcharge the expanded or foam cellular plastic pattern is burned out ordecomposed and in any event gasified and the thus formed gases passoutwardly through the porous incombustible layer surrounding thecellular plastic pattern and separating the same from the moldingmaterial, the surrounding incombustible layer may be such as to preventpassage therethrough of alloying or other materials which had beendistributed throughout the gasifiable plastic pattern. The porous layerthus may be traversed by the gases formed, for instance, by pyrolysis ofthe cellular plastic but will retain and prevent passage therethrough ofthe particles of the alloying or the like material in the mold, whichparticles of alloying or the like material will thus be-incorporated in,or react with, the casting charge.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

FIG. 1 is a perspective view of a gasifiable casting pattern accordingto the present invention;

FIG. 2 is a cross sectional view taken along lines ll-ll of FIG. 1;

FIG. 3 is an elevational view partially in cross section of a castingpattern for a radiator, according to the present invention;

FIG. 4 is a cross sectional view taken along lines IVIV of FIG. 3;

FIG. 5 is an elevational cross sectional view of a casting moldincorporating the casting pattern of FIGS. 1 and 2.

FIGS. 6-10 will serve primarily to illustrate embodiments of the presentinvention which encompass a gasifiable feeder head;

FIG. 10 is a fragmentary, elevational, cross sectional view of yetanother embodiment of the present invention.

The casting pattern 1 which is illustrated in FIGS. 1, 2 and 5 may serveas an example for producing a casting in accordance with the presentinvention without requiring a core, while at the same time providing thecasting with hardened surface portions in the area of the wheel body.Furthermore, as illustrated in FIG. 5, the casting will be produced inaccordance with the present invention so as to be substantially free ofcavities and pipings.

The upwardly extending portions 2, as shown in FIG. I, serve forreliable attachment of the risers and feeding conduits shown in FIG. 5.

As illustrated in FIG. 2, the gasifiable foamed plastic pattern 1carries a porous layer or coat 3 which covers the entire outer surfaceof plastic pattern 1. Incorporated and substantially evenly distributedthroughout foam cellular plastic pattern 1 may be alloying materials orother materials which will act on the molten casting charge when thesame is introduced into the mold so as to gasify and replace the plasticpattern. Interposed between the layer 3 of solid material, which remainssolid at the temperature of the molten casting charge and whichpreferably will be gas permeable at such temperature, and the gasifiablemember 1 may be a layer 4 of a material adapted to act on and toinfluence the surface portion of the casting during formation of thesame, for instance to increase the hardness of the surface portion.

FIGS. 3 and 4 illustrate one of the relatively rare cases when byproceeding in accordance with the present invention it is neverthelessdesirable to use a core.

As illustrated, the outermost layer 31 as shown in FIGS. 3 and 4,consists of a solid material which will remain solid at castingtemperatures and layer 31 contacts the outer surface of the gasifiablecellular plastic pattern 32. The core consists of a cellular plasticbody 33 and a layer 34 interposed between cellular plastic core 33 andcellular plastic pattern 32. Layer 34 consists of a material of low heatconductivity so that upon introduction of the molten casting charge andreplacement of gasifiable plastic pattern 32 by the casting charge, heatpenetration toward the gasifiable cellular plastic core portions 33 willbe considerably retarded, namely for a sufficient length of time so thatgasification of plastic core bodies 33 will take place only after theportion of the casting charge adjacent to layer 34 has been solidifiedand has become shape-retaining and self-supporting. Such corescontaining a gasifiable body are particularly suitable for castingswhich include relatively thin walls and which are formed with one ormore inner cavities access to which is relatively difficult.

FIG. illustrates the casting pattern of FIGS. 1 and 2 incorporated in amolding arrangement which includes a shell 51, mold body 52, open feederfunnel 53 and feeder 54 with riser 55. Feeding funnel 53, feeder 54 andriser 55 consist, initially similarly to pattern 1, of gasifiablecellular plastic material and feeding funnel 53 and feeder 54 aresurrounded by a layer of heat insulating material 56. The foamedcellular gasifiable plastic pattern again may have incorporated thereinsuitable alloying or treating materials for acting on or reacting withthe casting charge. Heat insulating layers 56 may consist of the porousgas permeable solid material which remains solid at casting temperaturesas described further above. The spherical blind riser 57 which is alsosurrounded by heat insulating layer 56 is formed with a small cutout atits upper portion which will serve for maintaining the elevatedtemperature of the melt for somewhat longer period of time. Theconstriction underneath spherical riser 57 will facilitate breaking offthe material which has solidified in riser 57.

It will be understood by those skilled in the art that many variationsof these auxiliary devices are possible and are within the scope of thepresent invention. Feeder and riser arrangements which are surrounded byheating means, usually providing heat by an alumino-thermic or the likeprocess, or by insulating materials have been known for a long time.However, up to now these elements had to consist of pressure resistant,hard, ceramic hollow bodies which had a relatively limited heating orinsulating effect and were quite expensive, while, according to thepresent invention, these members will consist of a form of gasifiablecellular plastic material which is covered with a layer of suitableinsulating material or the like.

Thus, in accordance with the present invention, by preforming feeders,risers and the like of gasifiable cellular plastic materials, which maybe joined to the casting pattern of the same type of materials, it ispossible to utilize layers of insulating materials which are highlyinsulating and relatively inexpensive although affording less pressureresistance, such as layers of mineral wool, and the like.

The materials which may be used for forming the solid gas permeablelayer 3 and which also may be used for forming the heat insulating layer56, are conventional materials which are, per se, known in the art. Heatresistant materials which are porous or which will become highlypermeable to gas when exposed to the temperature of the molten castingcharge are highly suitable for the first purpose. These materialsinclude diatomaceous earth or kieselguhr, asbestos, synthetic mineralfibers such as mineral wool, fire clay, clay, pumice, bentonite,perlite, vermiculite and the like, to which quartz sand or a similarmaterial may be added if desired. As binding agents for these mineralmaterials may be used thermo-setting or preferably cold settingsubstances such as plaster of Paris, cement, starch or synthetic resins,the latter being preferred. In a most simple manner, the layer is formedby preparing a suspension of the mineral material and binding agent inwater, to which suspension a suitable wetting agent and/or film formingagent may be added and which is then applied to the cellular plasticpattern, for instance, by hand, spray gun, immersion or other methods.The coating or layer will require only a short period of air drying, butit need not be subjected to a special drying process and may be allowedto stand in wet condition. The thickness of the coating preferably willnot exceed 6 mm. and more preferably will be between 2 and 5 mm. Theoutside of the layer or coating may remain in rough and unevencondition. It is a further advantage of the abovedescribed coating thatit is possible to incorporate therein without difiiculty materialswhich, when coming in contact with the casting charge, will affect thesurface properties of the casting. Moreover, it is possible to form alayer of a materinna al which will favorably affect the properties ofthe casting between the cellular pattern and the heat-resistant coating.Such layer, for instance, may be applied to the surface of the cellularplastic pattern prior to forming the heat resistant layer thereon.

In the production of castings which are required to have particularlyhard, wear-resistant surface portions, such as rollers and cam shafts,such treating layer or coating may consist of graphite, tellurium orferrosilicon, in other cases, particularly when producing light metalcastings, a treating layer of silicon or sulfur frequently will be foundadvantageous for improvement of the surface quality of the casting.

The specific material of which the heat resistant gas permeable layer isto be formed will depend on the type of casting which is to be produced,such as whether an aluminum casting is to be produced at about 700C. ora steel casting at about 1,500C.

For instance, in case of a casting to be formed of a metal having a highmelting point, the heat resistant porous layer may be formed of amixture of about percent by weight of unblown perlite, about 5 percentof water glass (aqueous solution containing 30 percent by weight ofsodium silicate) as binder and about 10 percent by weight of groundgraphite.

Water which may contain a wetting agent and a film-forming agent isadded in an amount sufficient to form a stiff paste which may be easilyapplied to the cellular casting pattern by hand and which dries quicklyand adheres well to the surface of the cellular plastic pattern. When itis desired to apply the layer by dipping or spraying, then a greaterquantity of water is added so as to achieve the desired consistencywhich is best suitable for the respective manner of applying the paste.

The perlite in the above-described mixture may be replaced by similarproportions of mineral wool, kieselguhr, ground pumice and the like.

The water glass binder may be replaced by a starch solution or asuitable solution or dispersion of synthetic resin.

The graphite may be suitably replaced by ferro-silicon or sillCOl'l.

The materials which may be incorporated in the heat resistant layer orwhich may be interposed between the heat resistant layer and the surfaceof the cellular plastic pattern, may either be mixed into the mass ofwhich the heat resistant layer is formed, or may be applied as anintermediate coating, for instance dispersed in alcohol or watercontaining a wetting agent and/or film forming agent.

As has been described above, it is possible according to the presentinvention to introduce into the casting charge while the same is fillingthe space originally occupied by the cellular plastic pattern, at leastone additional material which will serve to influence metallurgicallythe material of the cast workpiece. This is done by employing thecellular plastic material as the carrier for introducing such material.

The material which is intended to have a metallurgic effect on the meltor casting charge, or to alloy with the same, may be distributed asevenly as possible in the plastic material prior to blowing of the same,so that as a result of the expansion of the plastic material, an evendistribution of the added materials will be accomplished in the cellulargasifiable plastic pattern.

The gasifiable expanded plastic material which contains the evenlydistributed additional material may also be used to form the pouringsystem of the mold. Thus, for example, to influence the graphiteformation in cast-iorn alloys, materials such as ferrosilicon or nodulargraphite-forming elements such as magnesium and corium may be added.Powdery substances may also be added to the expanded plastic for eitherpreventing or promoting the solidification of cast-iron alloys in theform of white cast iron, for example magnesium and silicon (preventives)or sulfur and tellurium (promoters).

Furthermore, alloying constituents, such as vanadium, molybdenum and thelike may be introduced into the melt in accordance with the presentinvention.

Such alloying materials, or other materials which serve to influence thequality of the casting formed of the molten casting charge, are usuallyadded in such quantities that, with reference to the weight of thecasting, the alloying metals are present in an amount of up to 1percent, silicon in an amount of up to 0.8 percent and magnesium in anamount of up to 0.1 percent. In order to incorporate such proportions ofadded material in the casting, when employing the gasifiable expandedplastic pattern as carrier, the expanded plastic may contain up to 500percent of its weight of alloying metal or silicon, or up to about 50percent of its weight of magnesium, based on the weight of the expandedplastic.

In order to achieve a uniform distribution of such added alloying orother material in the expanded plastic, the additional material may beincorporated in the preexpanded granulate or in the monomers of theplastic. In the latter case, the added material may be distributedhomogeneously, prior to the polymerization, in one or more of themonomers prior to their admixture, or in the monomer mixture. The addedmaterial should be introduced in finely sub-divided form. This lastprocedure is particularly advantageous because it will result in a veryeven distribution of the added material, for instance an alloyingconstituent, in the expanded plastic.

If, in customary manner, the expansion of the plastic polymer will becarried out with the help of a suitable expanding agent under theinfluence of the super-heated steam, then certain difficulties areencountered when the added material, for example magnesium in powderform, is attacked by water. If, on the other hand, the added material isintroduced into the monomeric resin, then the material which issensitive to steam will be distributed very homogeneously in plasticexpanded with the use of steam and apparently remains protected againstattack by water due to the plastic material surrounding each of theparticles of magnesium or the like.

Referring now to the heat barrier or layer of low thermal conductivity,such as layer 34 of FIGS. 3 and 4, very good results are obtained in thecase of aluminum castings with layers formed of one part by weight of apolyvinylpropionate resin dispersion containing about 50 percent byweight of resin and 50 percent by weight of water, two parts by weightof lithopone, two parts by weight of white cement and three parts byweight of water with the addition of a small amount of a wetting agent.

The thickness of the thus formed dry layer of low thermal conductivitypreferably will be about 2 3 mm. and its weight about 300 grams persquare meter. However, these quantitative date should not be consideredas limiting the invention since innumerable variations may be made forspecific purposes. For instance, a metal powder or metal flakes and thelike may be incorporated in the layer, depending on the castingtemperature. The heat insulating layer 56 which primarily covers thecellular plastic material which is located in place of the riser andfeeder conduits, preferably will consist of a material of the type whichis suitable for forming layers 3 or 31, and very good results areachieved with respect to forming such porous layer by using thereformineral wool and a smoothening and binding agent such as bentonite.However, layers 56 preferably will be considerably thicker than layerssuch as layers 3 and 31.

The casting method of the present invention is not limited to anyspecific casting charge or material. It is possible to cast according tothe present invention substantially all casting metals such as bronze,light metals, iron, steel, heavy metals, as well as glass and silicatemelts (quartz), molten A1 0 SiC and the like. Is is of course requiredthat the melt will be sufficiently fluid within a temperature rangewhich will be sufficiently above the decomposition or gasificationtemperature of the foam plastic pattern, and the last conditiongenerally is met by a temperature of about 400C. Furthermore, it is ofcourse desirable that there should be as little reaction as possiblebetween the molten charge and the porous heat resistant layer or thelayer of low heat conductivity which covers the plastic pattern.

The plastic pattern according to the present invention, with the porouslayer thereon, is also suitable for forming castings in a mold bodyconsisting of loose sand without binder, for instance of free flowingquartz sand.

The incorporation of reactants such as alloying elements in the cellularplastic pattern has the great advantage that, for instance, startingwith a casting charge of regular pig iron, a cast body of alloyed metalcan be produced. The loss of the usually valuable reactants or alloyingmaterials is insignificant and can be further reduced by using theporous heat resistant layer interposed between the cellular plasticpattern and the mold body. When it is desired to influence the hardnessor other qualities of only the surface portion of the casting, then suchreactants are preferably applied as a thin layer or incorporated in athin layer on the surface of the cellular plastic pattern, as has beendescribed further above.

It is also possible according to the present invention to have theclosed cells of the cellular plastic pattern filled with a gaseoussubstance which will affect the quality of the casting. Thus, the cellsmay be filled with a gas which does not support combustion, e. g.nitrogen, carbon dioxide, halogenated hydrocarbons such as CF -CCI CFCClF and similar materials which are known by the trade name Freonc."Thereby it will be achieved on the one hand that combustion of thecellular plastic is prevented and consequently the amount of gas whichhas to be removed upon gasification of the plastic is reduced and, onthe other hand, it is possible in this manner to carry out the pouringof the casting charge in a protective gas atmosphere. It is alsopossible, according to the present invention, to incorporate gaseoushalogens such as chlorine in the expanded plastic, i.e. in the cellsthereof which halogens, particularly chlorine, will react advantageouslywith certain light metal melts, such as a casting charge of aluminum.Particularly the type of heat resistant layers or coatings which becomeporous only when subjected to heat, will permit the storing of thecellular plastic patterns covered with such heat resistant layer for aconsiderable length of time, without loss of the gas incorporated in theplastic pattern.

In general, cores are not required in connection with patterns made ofgasifiable expanded plastic material. If, however, in exceptional casessuch cores are required due to poor accessibility of interior recessesof the plastic pattern, then the cores may be incorporated when foamingthe expanded plastic patterns or they may be inserted thereafter. Forthis purpose it is possible to use not only cores made of conventionalmaterial, i.e. bonded sand and the like, but also cores which consist ofgasifiable expanded plastic, provided that the gasifiable expandedplastic core is surrounded by a solid layer of low thermal conductivity,a so-called heat barrier layer, which will retard the transmission ofheat from the melt to the expanded plastic core until after the meltlayer adjacent the core, i.e. outwardly and adjacent of the solid layerof low heat conductivity, has solidified. Due to the high temperature ofthe casting charge, the core will then be gasified and a recess willremain in the casting, the latter being covered adjacent to such recessby the barrier layer which can be easily blown ofi or otherwise removed.

Such barrier layer may consist of gypsum, clay, magnesium, calcium oxideor similar materials with hydraulic or organic binders such as polyvinylacetate resin, starch and the like, or including metal powders or metalflakes, and the heat barrier layer may be applied to the expandingplastic core in the same manner as the heat resistant porous coating isapplied to the expanded plastic pattern. Usually a thickness of thebarrier layer of a few millimeters will be sufficient for retarding heattransmission therethrough to such an extent that the core will begasified only after the portion of the charge adjacent to the barrierlayer has solidified.

It is possible to make not only the casting pattern of gasifiableexpanded plastic, but also the pattern for ingate, ventilation andconnecting conduits and/0r feeder heads (so-called blind risers), and toadhesively adhere the expanded plastic pattern to the expanded plasticmaterial of such conduits or feeders, either during the foaming processor thereafter. The term feeder is to be understood to denote additionalstorage space for the melt in the mold, i.e. additional space which canbe filled with molten charge. Such an additional space is frequentlydesirable in order to prevent hole or piping formation in metals whichhave a great tendency to shrink.

Hitherto parts of the molding system being particularly susceptible toshrink hole formation were provided with heating means or heatinsulating means by introducing suitable materials into the mold cavityafter having removed a conventional pattern. Therrnite mixtures wereused as heating means and hard burned ceramical materials which werebrittle, rather expensive and of relatively limited effect served asinsulating material. The coating provided according to the inventionrepresents a considerable progress in this respect, as it can be appliedwithout difficulty near or at all critical points of the pattern in anydesired thickness in order to secure the insulating effect required inevery particular case. The thickness of the coating may amount to 20'mm. or more. if required, the insulating effect can be increased byconventional heating means. The insulating portions of the coating mayconsist substantially of the above mentioned mineral fiber materials,i.e. asbestos or synthetic mineral fibers. Coatings of this kind have byfar better insulating effects than the hollow ceramic bodiesconventionally used for this purpose. In spite of the relatively loosestructure of such fibrous materials no difficulties arise when embeddingthe pattern, as all forces or stresses occurring thereby are absorbed bythe expanded plastic pattern. The gasifiable patterns are not onlysuited for molding metals but also for molding other melts, as forexample glass and silicate melts and the like provided that theircasting temperature is sufficiently higher than the decompositiontemperature of the expanded plastic material.

As an example only without, however, limiting the invention the solidcontent of the intermediate coatings 4 only comprise in percent ofweight: 75 95 pulverized silica, -8 ground graphite, 1-5 water glass, upto 3 bentonite, and A1 0 at the balance.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofmolding arrangements differing from the types described above.

While the invention has been illustrated and described as embodied in aningot mold arrangement, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A core member for use in forming a cavity in a metal casting,comprising a body consisting of an expanded plastic material which isgasifiable on subjection to a molten casting charge and havingsubstantially the configuration of the cavity in the article to be cast,and a layer of refractory material covering the entire exposed outersurface of said body for preventing contact between said casting chargeand said body and which remains solid and gas permeable at the elevatedtemperature of a molten casting charge.

2. A core member for use in forming a cavity in a metal casting,comprising a body consisting essentially of a gasifiable member havingsubstantially the configuration of the cavity in an article to be castand adapted to be gasified at the elevated temperature of the moltencasting charge and a layer of heat resistant material covering theentire outer surface of said body which is exposed to molten metal forpreventing contact between said casting charge and said body, said layerbeing gas permeable and retarding the transfer of heat from a moltencasting charge to said gasifiable member until the melt adjacent saidcore has solidified.

3. The core member set forth in claim 2 wherein said body consists of anexpanded plastic material which is gasifiable substantially withoutresidue when subjected to the molten casting charge and said heatresistant material is substantially incombustible at said temperature.

2. A core member for use in forming a cavity in a metal casting,comprising a body consisting essentially of a gasifiable member havingsubstantially the configuration of the cavity in an article to be castand adapted to be gasified at the elevated temperature of the moltencasting charge and a layer of heat resistant material covering theentire outer surface of said body which is exposed to molten metal forpreventing contact between said casting charge and said body, said layerbeinG gas permeable and retarding the transfer of heat from a moltencasting charge to said gasifiable member until the melt adjacent saidcore has solidified.
 3. The core member set forth in claim 2 whereinsaid body consists of an expanded plastic material which is gasifiablesubstantially without residue when subjected to the molten castingcharge and said heat resistant material is substantially incombustibleat said temperature.